What is: TypeError: xml is null

What is: TypeError: xml is null


Can anyone help with this situation? Please?
When I am in Edit mode, Script, on a form and attempt to access a field On Update script, I get a "TypeError: xml is null", and the "loading..." icon freezes. It never loads the script. I must refresh to release.
How do I debug this script if it won't load?
What does the error message mean?




Any assistance will be greatly appreciated.

Frank P.